basic question about avature

[Technoman]

I have purchased a mybb theme and when I try and add different avatures to it by uploading, sometimes they have a white background and YES I know in order to get rid of it you need to tranform the avature into transparent for it not to have a white around it..

Is there away to tranform all avatures on the site or some type of method or plug-in cause on this theme sometimes with different avatures it really makes avatures look ugly